Process for the production of particle board using cross-linked xanthomonas colloid in the glue mixture

ABSTRACT

A PROCESS FOR PRODUCING PARTICLE BOARD IN WHICH A XANTHOMONAS HYDROPHILIC COLLOID AND A CROSS-LINKING AGENT FOR SAID COLLOID ARE ADDED TO THE GLUE MIX. THE GLUE MIX IS THEN SPRAYED ONTO WOOD CHIPS WHICH ARE COMPRESSED AND HEATED TO FORM THE FINISHED BOARD. BY USE OF THE XANTHOMONAS COLLOID AND THE CROSS-LINKING AGENT, THE AMOUNT OF THE GLUE REQUIRED FOR FORMATION OF THE PRACTICE BOARD IS REDUCED.

United States Patent 3,736,275 PROCESS FOR THE PRODUCTION OF PARTICLEBOARD USING CROSS-LINKED XANTHOMONAS COLLOID IN THE GLUE MIXTURENicholas J. Iammarino, San Diego, Calif., assignor to Kelco Company, SanDiego, Calif. N0 Drawing. Filed Nov. 18, 1971, Ser. No. 200,196 Int. Cl.C08g 51/18 U.S. Cl. 260-17.? 7 Claims ABSTRACT OF THE DISCLOSURE Thisinvention pertains to an improved procedure for forming particle board.Further, the invention pertains to a procedure for forming particleboard which permits the use of a reduced amount of glue.

Various procedures are known to the prior art for forming particleboard. In general, all of these procedures produce particle board bycuring a mixture of a thermosetting resin in admixture with wood chipsunder pressure to produce a coherent structure in which the wood chipsare bonded together by the resin. Prior art procedures for formingparticle board may be further categorized in terms of caul processes andcaul-less processes. The caul processes utilize a metal plate which istermed a caul. This plate is passed under a bin containing wood chipsthat have been wetted with a glue composed of a urea formaldehyde resinin water. There may also be present in the glue a catalyst to promotethe curing of the urea formaldehyde resin.

In forming the particle board, a first layer of wood chips and resin isgenerally laid down on the caul plate. This first layer is termed theface mix and will form a face of the finished particle board. After theface mix is laid down on the caul, a second layer of wood chips andresin is then laid down on top of the face mix. This second layer istermed the core mix since it will form the core of the finished particleboard. Following this, a third layer of wood chips and resin is laiddown on top of the core mix. The third layer is also a face mix and willform the opposite face of the finished particle board. After the facemixes and core mix have been laid down on the caul plate by pass ing theplate under several bins which contain Wood chips wetted by a ureaformaldehyde resin in water, the several layers of wood chips and resinwhich have been deposited on the caul plate are termed a biscuit.

Following formation of the biscuit, a plurality of caul plates areloaded into a press. The presses employed in the caul process may bequite complex and receive a large number of individual caul plates. Inoperation of the press, the caul plates are generally individuallyloaded into a press from the top to the bottom of the press. Theindividual caul plates and biscuits are held apart in the press byseparators and, when fully loaded, a press of this type may contain asmany as 20 caul plates.

After loading of the press, the biscuits supported on the caul plateswithin the press may all be compressed at the same time. The spacerelements carried on each of the caul plates will determine the height ofthe individual particle boards after their formation by pressing of thebiscuits. By way of example, a biscuit which has an initial thickness ofabout 3 /2. inches may be pressed down to a thickness of about 0.7 inch,or a biscuit which has an initial thickness of 7 inches may be presseddown to a final thickness of approximately 1% inches. During thepressing operation, the biscuits are generally heated to a temperaturesuch as 200- 400 F. while being compressed at about 20 to 60 p.s.i. Theexact conditions utilized in the pressing and curing of the biscuits toform the particle board may be varied depending upon a number ofconditions, such as, the presence or absence of a curing catalyst, thenature of the curing catalyst, the type of urea formaldehyde resinsystem employed, the wood species used in forming the chips, the size ofthe chips, and the pressure and temperature limitations of the press.

After pressing of the biscuits at an elevated temperature, the press isthen opened and the particle boards are removed from the caul plates.The caul plates are also removed from the press and allowed to cool, ifnecessary, and then re-used in the overall process by receiving woodchips and resin from bins to form biscuits, etc. After removal of theparticle boards from the caul plate, they may be finished in aconventional manner before being shipped. The various conventionalfinishing operations can include, for example, cutting, sanding,coating, sizing, stacking, etc.

The caul-less process used for forming particle boards is quite similarto the caul process but with one important difference. Caul plates arenot used in the caulless process for supporting the biscuits. Rather, amixture of wood chips and resin are deposited on a supporting surface,such as a perforated belt, to form the biscuits. The biscuits may thenbe moved onto press plates which support the biscuits during thepressing operation. After pressing and curing to form the particleboards, the boards may be subjected to standard finishing operations asenumerated above.

In any of the various procedures utilized by the prior art for formingparticle board, it is necessary that the wood chips be sprayed with aglue composed of a thermosetting resinin water. The resin system whichis almost universally employed in forming particle board utilizes a ureaformaldehyde resin and optionally a curing catalyst. The glue-watermixture is sprayed onto the wood chips which are contained in a bin. Inorder to obtain a satisfactory distribution of the glue throughout thewood chips, it is necessary that the droplets of the glue-Water mixturehave a relatively small particle size. Typically, the size of theglue-water droplets may range in the order of about 1 mm. to about 20mm.

A problem which has plagued prior art processes for forming particleboard is the absorption of excess glue by the wood chips. This problemis particularly acute if the wood chips are derived from wood speciesthat are porous. In attempting to solve this problem, one suggestion hasbeen to size the wood chips with a thermoplastic resin to substantiallyreduce the porosity of the chips. Following this, the sized wood chipsare admixed with a thermosetting resin and treated in a conventionalmanner to form particle board. This procedure is illustrated by U.S.Pat. 3,287,479 to Edward A. Naudain.

Other attempts by the prior art to control the problem of excessabsorption of glue by the wood chips have involved the addition ofvarious thickeners to the glue mix, such as guar gum, locust bean gum,carboxymethyl cellulose, hydroxyethyl cellulose, starch, or variouscombinations of thickeners. These attempts have resulted in failuresince the addition of a thickener in any substantial amount to the gluemix produces an increase in the viscosity of the glue mixture. This, inturn, decreases the atomization efliciency of the glue mix as it isapplied through the spray nozzles to the wood chips. As a result, theglue mix is not properly distributed throughout the Wood chips and thewood chips are not uniformly bonded to each other to form the finishedparticle board.

In solving the problems of the prior art, as outlined above, I havefound that the addition of a Xanthomonas hydrophilic colloid inconjunction with a cross-linking agent in an amount sufiicient toproduce only a very minor increase in the viscosity of the systemproduces a substantial reduction in the absorption of the glue by thewood particles. Since this result is achieved with only a minor increasein the viscosity of the glue mix, there is little change in theatomization eificiency of the glue mix. Thus, the glue mix may bereadily applied through spray nozzles onto the wood particles to producea relatively uniform distribution of glue throughout the particles.

The Xanthomonas hydrophilic colloids used in my invention are colloidalmaterials which are produced by bacteria of the genus Xanthomonas.Illustrative of such colloidal materials is the hydrophilic colloidproduced by the bacterium Xanthomonas campestris. This colloidalmaterial is a polymer containing mannose, glucose, potassium glucuronateand acetyl radicals. In such a colloid, the potassium portion of thecolloid can be replaced by several other cations without any substantialchange in the properties of the colloid for purposes of the presentinvention.

A Xanthomonas colloid is a high molecular weight, exocellular materialwhich is prepared by a fermentation process utilizing a Xanthomonasbacteria, e.g., the bacterium X anthomonas campestris. Typically, thefermentation medium may contain glucose, an organic nitrogen source, aphosphate buffer and appropriate trace elements. The incubation may becarried out under aerobic conditions with agitation for a sufficienttime to produce the colloidal material.

After the fermentation is completed, the colloidal material may berecovered by precipitation from the fermentation mixture. Precipitationof the colloid is generally brought about by the addition of a loweralkanol, such as methanol. If desired, the fermentation beer may besubjected to filtration or centrifugation prior to the addition of thelower alkanol to cause precipitation of the colloid. The colloid, asprepared by the above procedure, will contain dead bacterial cells inadmixture with the colloidal material.

Various Xanthomonas colloids may be prepared by substituting other knownXanthomonas organisms for the bacterium Xanthomonas campersm's in theabove described process. Examples of other Xanthomonas organisms areXanthomonas carotae, Xanthomonas incanae, Xanthomonas begom'ae, andXanthomonas malvacearum.

Procedures for preparing a Xanthomonas hydrophilic colloid are describedin a number of prior patents, and do not form a part of my invention.The description of the manner in which a Xanthomonas colloid is preparedis merely to provide a better understanding of the invention.

In accord with my process, a small quantity of a Xanthomonas hydrophiliccolloid is added to the glue mix, which includes water, a ureaformaldehyde resin, and optionally a curing catalyst for the ureaformaldehyde resin. The quantity of Xanthomonas hydrophilic colloid mayrange from about 0.03 to about 2% by weight of the glue mix and ispreferably in the order of about 0.1% by weight of the glue mix. Theglue mix is generally contained in a vessel called the glue tank. Ifdesired, the Xanthomonas hydrophilic colloid can be added directly tothe glue tank. In most cases, however, this is not practical because theglue tank generally has a small capacity and contains about 300 lbs. ofmaterial. The production of particle board is a continuous process and,thus, materials are continuously added to and are continuously removedfrom the glue tank. For this reason, there is no advantage in having alarge capacity glue tank.

A preferred procedure is to add the Xanthomonas hydrophilic colloid to awaterline leading into the glue tank. The volume of the Waterline isgenerally larger than that of the glue tank in most installations andprovides a better opportunity for the Xanthomonas hydrophilic colloid togo into solution.

There is also added, in accord with my process, a crosslinking agent forthe Xanthomonas colloid. The crosslinking agent is a water-soluble saltwhich contains either ferrous or ferric ions. Ferrous or ferric ions ormixtures thereof react with the Xanthomonas hydrophilic colloid to forma cross-linked structure. Due to the shear in the system, thecross-linked structure is broken up as it is formed by reaction offerric or ferrous ions with the Xanthomonas colloid. The net result is adisrupted gel system within the glue mix.

By introducing both the Xanthomonas colloid and the water soluble saltcontaining a ferrous or ferric ion into the waterline leading to theglue tank, better contact is obtained between the Xanthomonas colloidand the ferrous or ferric ion. When both the Xanthomonas colloid andcross-linking salt are introduced directly into the glue tank, thepresence of other components Within the glue tank, e.g., the ureaformaldehyde resin and the curing catalyst for the resin, may interferewith the contact between the Xanthomonas colloid and the ferrous orferric salt. When this occurs, a disrupted gel is not formed to the samedegree as when the Xanthomonas colloid and the ferrous or ferric saltare added to a waterline leading to the glue tank.

The ferrous or ferric salt utilized in my process is added in an amountsufficient to provide an iron concentration ranging from about 7 partsper million to about 15% by Weight based on the weight of the dryXanthomonas hydrophilic colloid that is present. The ferrous ion reactswith the Xanthomonas hydrophilic colloid to give a relatively soft gel.In contrast, the ferric ion reacts with a Xanthomonas colloid to give arelatively hard gel.

The decision to use ferrous ions instead of ferric ions as across-linker or to use a mixture of the two will depend upon theequipment utilized in the particular plant for production of particleboard. If the plant equipment produces a relatively low degree of shear,the use of a ferric salt could produce plugging problems when the gluemix is ejected through the spray nozzles onto the wood chips. In thiscase, plugging could be alleviated by using a cross-linking salt whichprovided only ferrous ions or by increasing the concentration of ferrousions in the system while reducing that of the ferric ions. This wouldresult in formation of a softer gel which would have less tendency toplug the ejection nozzles.

Conversely, if the degree of shear generated by the equipment issufficiently high, it may destroy the softer gel formed by cross-linkingof the ferrous ion with a Xanthomonas hydrophilic colloid. This wouldresult in increased absorption of glue by the glue chips and wouldrequire increasing the amount of glue to produce satisfactory particleboard. To alleviate this problem, a ferric salt could be substituted forthe ferrous salt to produce a harder gel having a greater resistance toshear. Also, rather than to completely eliminate the ferrous salt,satisfactory results could be obtained in many cases merely byincreasing the content of ferric ions with respect to the content offerrous ions in the system.

In the previous caul processes for forming particle board, the weight ofglue solids required was about six to seven percent by weight based onthe weight of the wood chips. Higher glue levels were required in thecaulless process and ranged from about 12 to about 14% by weight of gluesolids based on the Weight of wood chips.

As a result of my invention, it is now possible to substantially reducethe level of glue solids required for the formation of particle board.Theoretically, if there were no loss of glue solids due to the capillaryaction of the wood chips in absorbing the glue, only about three to 3/z% by Weight of glue solids would be required based on the weight ofthe wood chips. My process does not completely eliminate the absorptionof glue by the wood particles. Thus, I have been unable to producesatisfactory particle board by using the minimum glue solidsconcentrations predicted from theory. I have, however, been able toachieve substantial economies by reducing the glue solids levels to farless than their present levels.

To generalize, in the application of my invention to existing caulprocesses, 1 have been able to produce satisfactory particle board withglue solids level of about 4.5 to about 6.0 percent by weight based onthe weight of the wood particles. In the application of my invention toexisting caul-less processes, I have been able to prepare satisfactoryparticle board at glue solids levels of about 4.8 to about 6.5 percentby weight based on the weight of the wood particles.

In using my process, the increase in the viscosity of the glue-watermixture applied to the wood particles is relatively minor. By relativelyminor, I refer to a viscosity increase in the order of about five toabout ten centipoises. Thus, if the viscosity level of the glue mixturewas already at 200 cps., the use of my process would result in anincreased viscosity of the glue mixture to about 205 or 210 cps. As aresult, the use of my process does not interfere to any appreciableextent with the atomization efiiciency of the glue-water mixture as itis ejected through nozzles onto the wood particles. The use of myprocess, therefore, provides a uniform distribution of the glue solidsthroughout the wood particles as required for uniform bonding of thewood particles in producing particle board.

In the use of my process, a certain amount of trial and error may beinvolved in achieving the optimum conditions for a particular plant. Todetermine the optimum conditions, it can first be assumed that the plantis operating at the glue solids level previously employed to produce aparticle board of a given strength. A small quantity of a Xanthomonashydrophilic colloid and a water soluble ferrous or ferric salt may thenbe added to the glue mixture in the manner described previously.Following this, the strength of the resulting particle board may bemeasured. Since the addition of the Xanthomonas hydrophilic colloid andthe cross-linking agent will increase the efiiciency of the glueutilization in the process, the strength of the particle board will begreater than that of the particle board previously produced. At thispoint, the glue level utilized in the process may be gradually reducedwhile continuously monitoring the resulting strength of the particleboard. In this manner, the optimum conditions, i.e., the exactconcentration of Xanthomonas hydrophilic colloid and the exactconcentration of the ferrous and/or ferric salt, are determined forproduction of satisfactory particle board at reduced glue solids levels.

My process, as described above, has particular application to theformation of particle board in which the binder is a urea-formaldehyderesin. However, my process may be used in the formation of particleboard using as the binder material any thermosetting water solubleresin. In such use, the Xanthomonas hydrophilic colloid andcross-linking agent are present in the amounts specified above, i.e.,about 0.03 to about 2% of the Xanthomonas colloid based on the weight ofthe glue mix and about 7 parts per million to about 15% by weight of aferrous or ferric salt based on the dry weight of the Xanthomonascolloid.

My process may also be utilized in forming particle board in which an insitu resin system is used as the binder. Such resin systems are knownand the particular makeup of the resin system is not critical to myprocess. Thus, for example, appropriate in situ resins includeureaformaldehyde-melamine, phenolic-melamine,urea-formaldehyde-phenolic, or urea-phenolic-melamine resin systems. Inapplying my process to the use of an in situ resin system, the resinsand water may be mixed in a tank and then admixed with a Xanthomonascolloid and a ferrous or ferric salt, as described above. My processpermits the use of in situ resin binders which have previously not beensuitable for use in the formation of particle board. By the use of myprocess, the penetration of the wood particles by the resin may becontrolled and the amount of glue required may thereby be reduced. Also,by the use of my process, the tackiness of in situ resins may beincreased to provide better bonding of the wood particles in thepreparation of particle board.

In the use of my process, as described above, a polymerization catalystmay be present to promote the polymerization of the resin binder. Theacids given off by the wood particles in the formation of particle boardmy also act as a polymerization catalyst.

As described in the foregoing specification, my process has applicationto existing procedures, as described in the prior literature, forproducing particle board. By utilizing my process, the glue solidslevels required by prior processes may be reduced to achieve substantialeconomies in the production of particle board. The procedures presentlyutilized for formation of particle board do not have to be altered toany appreciable extent in the use of my process. Thus, my process can beapplied to the manufacture of particle board without any extensivemodification of existing plants and equipment.

What is claimed is:

1. A process for the production of particle board in which wood chipsare treated with a glue-water mixture containing a urea-formaldehyderesin and thereafter formed into particle board by means of heat andpressure, the improvement comprising adding to the glue-water mixturefrom about 0.03 to about 2.0% by weight of the glue mixture of aXanthomonas hydrophilic colloid and from about 7 parts per million toabout 15% by weight based on the dry weight of said Xanthomonas colloidof a water soluble salt or mixture of salts containing ferrous ions,ferric ions, or mixtures thereof, to form a disrupted gel structurewithin said glue mixture and thereby to permit the reduction in the gluesolids level in the production of particle board.

2. The process of claim 1 wherein said Xanthomonas hydrophilic colloidis a Xanthomonas compestris colloid.

3. The process of claim 1 wherein said Xanthomonas colloid and saidwater soluble salt are first admixed in water and then added to saidglue-water mixture.

4. A process for the production of particle board in which wood chipsare treated with a glue-water mixture containing a water solublethermosetting resin and thereafter formed into particle board by meansof heat and pressure, the improvement comprising adding to the gluewatermixture from about 0.03 to about 2.0% by weight of the glue mixture of aXanthomonas hydrophilic colloid and about 7 parts per million to about15% by weight based on the dry weight of said Xanthomonas colloid of awater soluble salt or mixture of salts containing ferrous 1ons, ferricions, or mixtures thereof, to form a disrupted gel structure within saidglue mixture and thereby to permit the reduction in the glue solidslevel in the production of particle board.

5. The process of claim 4 wherein said Xanthomonas hydrophilic colloidis a Xanthomonas campestris colloid.

6. The process of claim 4 wherein said resin is composed of an in situpolymerization resin system.

7. The process of claim 6 wherein said resin is aureaformaldehyde-melamine resin.

References Cited Chem. Abst., vol. 66: 4740Tr, Aqueous Polymeric CoatingCompositions, Tenneco Chemicals, Inc.

WILLIAM H. SHORT, Primary Examiner E. WOODBERRY, Assistant Examiner US.Cl. X.R. 264-l22

